The disclosed invention is directed generally to computer data storage digital audio tape (DAT) systems for digital storage, and is directed more particularly to techniques for assembling data read from a DAT tape into data groups with reduced buffer management.
Digital audio tape (DAT) technology, which was developed for audio programming, has been adapted for storage of computer data. An example of a format for the storage of computer data utilizing DAT technology is the American National Standards Institute (ANSI) Digital Data Storage (DDS) standard, presently in draft form ("PROPOSED AMERICAN NATIONAL STANDARD HELICAL-SCAN DIGITAL COMPUTER TAPE CARTRIDGE 381 mm (0.150 in) FOR INFORMATION INTERCHANGE," ASC X3 Project No. 668-D).
The characteristics that have made DAT technology attractive for computer data storage include high capacity, high transfer rate capability, relatively small media size and low media cost, and the adaptability of DAT technology to conform with personal computer storage device form factors including the 51/4 and 31/2 inch forms.
The use of DAT technology for storage of computer data can be achieved by application of a data storage format, such as the above-referenced ANSI DDS format, to the DAT format. In particular, the DAT physical track format is retained, but the contents of the information stored in the tracks is in accordance with the computer data storage format.
As is well known, reading a tape with a DAT system requires that the digital data stream produced by reading a computer data storage DAT tape must be organized in accordance with a predetermined formatting convention, for example, for transfer to a host computer. For example, pursuant to the ANSI DDS standard, the digital data stream must be broken into frames which are combined into groups, where a frame comprises 2 tracks and a group includes 22 or 23 frames, depending on the level of error correction implemented. The frames in a group must be arranged in an ordered sequence, which may be different from the sequence of the frames in the data stream.
In a data storage DAT tape, each frame includes a header that identifies its relative position within its group, and computer storage DAT systems typically utilize such headers with buffer management for assembling frames into groups. For example, a two step process might be used. Each frame is transferred into a distinct frame memory, and the next step is to move the frame to its proper location in a group buffer which would typically be in a separate memory. Considerations with such processing include the use of a separate frame memory having sufficient capacity to store at least two frames to allow for processing of a frame that has been completely read in while another frame is being read into the frame memory, and the complexity of the associated control hardware (e.g., parity generation, storage and checking).